The dreaded communal salsa bowl. At a large gathering or party, who knows how many people have double dipped or even triple dipped?! It is a well-known idea that double-dipping is nasty and should only occur when there is only one person eating from the dish. I wanted to know more of the science behind double dipping and if it is worth it. Personally, I think it is very likely that double-dipping adds bacteria to the food, since a person makes contact with the bacteria in their mouth and proceeds to put it back in the food.
Researchers at Clemson University set out to determine if double dipping adds germs and bacteria to food. The study was composed of three separate experiments to determine this answer. One of the experiments they performed had eight people submerse crackers into water, with some taking a bite prior to dipping, in order to see if double dipping alters bacteria levels. After this experiment was performed, the concluding data shows significantly higher levels of bacteria when the cracker was bitten before dipped as opposed to the others who did not bite it prior to dipping it into the water. A “P” value is provided in the abstract of this experiment and is less than 5%. This means that given the values of the data, it is very unlikely that these results are a fluke, although they could still be due to chance. Initially it stands out to me that this particular experiment only had eight people in total, which reduces the reliability of the experiment.
The second experiment performed on this subject was similar, but tested the pH of common dips that are victims of double dipping- including salsa, chocolate sauce, and cheese sauce. The results remain consistent with the first experiment: there were higher levels of bacteria in the double dipped solutions than the untouched solutions. Although, the salsa had more bacteria than the chocolate sauce and cheese sauce solutions. This could either be a fluke or an experimental error, but there is no mechanism provided for why the salsa has higher bacteria.
These experiments were two of three performed in this study in order to find out whether double dipping makes a difference in bacteria in food or if it’s not a big deal. The third experiment was very similar to the second experiment, with consistent results as the preceding two. This is the only study I could find that had a reliable design. Although, the study could have been larger, the results remain consistent with my hypothesis that double dipping adds bacteria to a food dish.
Although the study concludes with elevated bacteria levels in double-dipped dishes, these are soft endpoints because it would only increase the level of bacteria in the food, which people believe could make them sick. Bacteria is everywhere, so there is no way to avoid consuming bacteria even if you do not double dip because there are many other ways these bacteria can be spread (e.g. coughing). With this study, the null hypothesis, that double dipping does not increase bacteria levels in food, is rejected due to the increase in levels of bacteria.
To summarize, double dipping does add more bacteria to food than is already there. In the end, it is not worth it to double dip because although you may not be affected, those who come after you will be affected also. Not to mention someone could have double dipped before you got there!